1. Field of the Invention
This invention is directed to a composition and method for removal of probing ink and negative photoresist polymer residue from a substrate, such as a silicon wafer. Mixtures including anisole, organic sulfonic acids, and aliphatic hydrocarbons containing 9 to 13 carbon atoms are used to strip hard to remove materials such as probing ink and cross-linked negative photoresist polymer residue. The composition and method achieve improved removal of these materials while significantly reducing metal corrosion.
2. Brief Description of the Prior Art
In the manufacture of semiconductor microcircuits it is necessary to mark defective microchips during the final electrical testing with an epoxy or polyurethane based ink on the finished silicon wafer to distinguish bad dies from the good dies. After the electrical test is done, sometimes it may be deemed necessary to clean the ink off the silicon wafer because of a wrong electrical test program, because bonding pads were misprobed, or for other reasons. This allows the silicon wafer be retested or reprobed with the necessary corrections. Conventional solvents such as alcohols, ketones and esters, or more aggressive heterocyclic solvents such as n-methyl pyrrolidone do not remove hard baked and cured epoxy type probing ink even at elevated temperatures and long process times.
Highly acidic or alkaline solutions and strong oxidizing agents on the other hand, such as fuming nitric acid, sulfuric acid/hydrogen peroxide, and tetramethyl ammonium hydroxide or other alkaline solutions may be effective in removing the ink, but they create corrosion difficulties and stain or destroy the sensitive alloys such as Al/Cu/Si in bonding pad areas of the wafer.
It is therefore highly desirable to provide an environmentally friendly ink removing process and a corresponding composition which in a reasonably short process time cleans only the cured probing ink without leaving any residue, and that is also safe to use on sensitive metal layers.
The present invention is also useful for removal of negative photoresist. Prior art resist removers are described in U.S. Pat. Nos. 4,165,294 and 4,992,108. These patents also describe organic sulfonic acids suitable for use in the present invention, and to that extent their disclosures are incorporated herein by reference.